A tapped transformer typically has, as described in Austrian patent 162,527, a plurality of taps connected to respective contact terminals arranged in annular arrays spaced apart in an insulating sleeve along the axis of the sleeve. Level with each such array is a contact ring and a respective radially extending bridge contact has an inner end that grips this ring and an outer end that can grip any one of the contact terminals of the respective array. These bridge contacts, which are described in some detail in U.S. Pat. Nos. 4,931,599, 4,935,586, and 4,939,319 of A. Bleibtreu, are in turn carried by a switching rotor so that they can be moved jointly to connect the inner rings to the selected outer contact terminals.
As described in German patent documents 1,193,145 and 2,354,173 of R. Heinz such a bridge contact comprises a pair of relatively displaceable and substantially identical jaws that are urged together by at least one spring to grip the inner contact ring and the respective outer contact terminal. The overall radial length of such a bridge contact is a function of the voltage of the system, and also of the number of terminals in each annular array. Thus different bridge contacts must be used for different systems.
In addition such bridge contacts and the contact terminals must be made to fairly close tolerances. If not the bridge contacts become canted and jam.